1. Field of the Invention
The invention relates generally to the formation of metal patterns on a plastic surface, and more particularly, but not by way of limitation, to the production of printed circuit boards.
2. Description of the Prior Art
The current practice for making conductive paths in such applications as printed circuit boards and integrated circuits generally falls into two categories. One is the etching from a completely conducting sheet of the areas desired to be non-conducting, which is generally referred to as a subtractive method. The other method, commonly known as the additive method, is to metal-coat a substrate while preventing metal contact with non-conducting areas. Such a coating process usually involves plating or vacuum deposition of metal. Simpler methods and less expensive materials are constantly being sought for such applications.
One particular group of materials which have been found promising for use as a substrate for such printed circuit boards are poly(arylene sulfide) materials which due to their stability at high temperatures, and their resistance to various chemicals, have found ever broadening areas of application.
U.S. Pat. No. 4,615,907 to Boeke et al., and assigned to the assignee of the present invention, discloses one technique for electroless plating of poly(arylene sulfide) surfaces which have been made water-wettable through laser treatment.
U.S. Pat. No. 4,486,463 to Rubner et al., and assigned to GTE Laboratories, Inc., discloses another process for plating poly(phenylene sulfide) articles. The Rubner et al. process is based upon creating a selective pattern of crystallization on the surface of the poly(phenylene sulfide) material, as is the present invention, but the process itself is very different. The Rubner et al. process plates the crystalline areas of the surface, whereas the present invention as described below plates the non-crystalline areas of the surface through a very different technique.
U.S. Pat. Nos. 4,540,620 and 4,527,219, both to Johnson et al., and both assigned to the assignee of the present invention, disclose that amorphous areas of a poly(arylene sulfide) surface can be made electrically conductive by doping the same with nitrosonium hexafluorophospate in concentrations on the order of about one to one and one-half percent in a solvent carrier. Example V of U.S. Pat. No. 4,540,620 discloses the use of an electron beam to form amorphous areas prior to doping. The doping of the amorphous areas in the '620 and '219 patents is done only with relatively low concentrations of nitrosonium hexafluorophospate, which are not sufficient to actually etch the amorphous areas of the substrate. The doping is done for the purpose of creating an electrically conductive surface. No plating of any kind was applied in the processes of the '620 and '219 patents, since they were directed to the production of electrically conductive patterns in the material so as to provide circuitry without the need for plating.
U.S. Pat. No. 4,540,631 to Boultinghouse, and U.S. Pat. No. 4,532,015 to Boultinghouse et al., both assigned to the assignee of the present invention, deal generally with electroless plating methods.